Card readers for reading magnetic data recorded on a card and recording magnetic data onto the card have been used widely. In industries such as financial institutions where card readers are used, so-called skimming in which the magnetic data of a card is illegally acquired using a magnetic head by a criminal attaching the magnetic head to a card insertion part of a card reader has become a large problem. The tricks used for skimming by criminals become more sophisticated year by year, and the situation in which a device for skimming such as a magnetic head for skimming (hereinafter, referred to as an “insert skimmer”) for reading the magnetic data of the card is attached to the inside of a card reader occurs. Therefore, various techniques for detecting that an insert skimmer has been inserted on the inside of a card reader have been proposed.
For example, JP-A 2016-110415 discloses a card reader comprising a capacitance sensor attached to a card passage which passes through a card inserted from an insertion port of the card. If an insert skimmer is attached to the card passage, it is detected as a foreign matter by the capacitance sensor, and a process such as notifying a predetermined alarm to the host device is performed.
If a host device on which a card reader is mounted is installed outdoors, or if a card is inserted in a card reader in a state in which snow or rain water are adhered to the card, there is the possibility that a liquid such as water will enter the card conveyance path. As described in JP-A 2016-110415, in a method for using a capacitance sensor to detect the attachment of an insert skimmer, it is necessary to discriminate between the case when the capacitance increased due to the entry of a liquid and the case when the capacitance increased due to the attachment of the insert skimmer.